Sonar adds silence. Normal behaviour?

I have a project consisting of 10 clips with different lengths. Each of them is supposed to be exported as a single wav file. But Sonar ignores their individual lengths when bouncing.
It considers always the longest clip even when this track is muted or not selected. That means every wav file shows the maximum length of this clip, in my case around seven minutes. The shortest clip has a length of two minutes, Sonar adds five minutes silence there.
 
My options would be:
 
mark a specific area in the time ruler as shown in this video at 2:00  https://www.youtube.com/watch?v=lRbRr-0wwjQ
                        or
create a single project for every audio clip
                        or
start exporting with the longest clip, delete it and continue with the next shortest ...  
 
That happens in Sonar 8.5 and X1, both PE. Is this a bug or normal behaviour? I still hope to find a hidden button or slider somewhere in the settings or export dialog box. ;)